1. Field of the Invention
The present invention relates to a display apparatus and a control method therefor.
2. Description of the Related Art
In recent years, a liquid crystal display apparatus is becoming mainstream as an image display apparatus. A liquid crystal display apparatus is a display apparatus which displays images as a result of a liquid crystal panel transmitting or shielding light emitted from a backlight (light emitting apparatus).
With a liquid crystal display apparatus, a light emitting diode (LED) is often used as a light source of the backlight.
Moreover, certain liquid crystal display apparatuses can control the emission brightness of the backlight for each divided region obtained by dividing a region of a screen. This kind of control is hereinafter referred to as “local dimming control”. The local dimming control can be performed, for example, with a liquid crystal display apparatus including a backlight provided with an LED for each divided region.
Moreover, with a liquid crystal display apparatus, brightness correction processing is performed using a measured value (sensor value) of the brightness sensor provided to the liquid crystal display apparatus in order to cause the emission brightness of the backlight to reach the target value.
The brightness control processing in a liquid crystal display apparatus capable of performing local dimming control is now explained in detail.
FIG. 10A is a diagram showing the state of the brightness correction processing. In the examples shown in FIGS. 10A to 10C, the respective regions obtained by dividing the region of the screen with a broken line are the blocks. The block and the foregoing divided region (one unit of local dimming control) may be the same or may be different. In order to perform the brightness correction processing, the liquid crystal display apparatus is provided with a brightness sensor for measuring the emission brightness of the backlight corresponding to each of blocks. The brightness correction processing is performed for each block. Specifically, for each block, the emission brightness of the backlight corresponding to that block is corrected by using the measured value of the brightness sensor corresponding to that block (emission brightness corresponding to that block). Measurement of the emission brightness by the brightness sensor is performed by turning OFF the LED of the blocks other than the block to be measured (only turning ON the LED of the block to be measured) in order obtain an accurate measured value (accurate emission brightness). Thus, it is difficult to simultaneously implement the brightness correction processing of a plurality of blocks, and the brightness correction processing of each block is often implemented in a predetermined order (specifically, the order shown with the arrow in FIG. 10A).
Nevertheless, with this kind of liquid crystal display apparatus, there are cases where a change occurs to the temperature of the backlight. For example, when there is a chip on a substrate located near the backlight, the temperature of the backlight will change due to the heat generated from that chip. Moreover, if the influence of the generation of heat from the chip on the temperature of the backlight differs among blocks, an uneven temperature distribution will occur in the backlight (there will be a temperature difference of the backlight among the blocks). For example, when a chip (heat source) is provided only to certain blocks, an uneven temperature distribution will occur in the backlight (FIG. 10B). Moreover, even in cases where a chip is provided to each block, since the amount of heat generated by the chip will change depending on the processing load of that chip, an uneven temperature distribution may occur in the backlight. Since LEDs and brightness sensors possess temperature characteristics, when the foregoing temperature distribution (temperature unevenness) occurs, it is not possible to perform an accurate correction, and brightness unevenness caused by the temperature of the backlight will occur.
Conventional technology for resolving the foregoing problems is disclosed, for example, in Japanese Patent Application Publication No. 2007-298957. Specifically, with the technology disclosed in Japanese Patent Application Publication No. 2007-298957, the temperature of the region of the screen is measured with a plurality of temperature sensors, and, when there is a considerable temperature difference between a certain region of the screen and the other regions of the screen, such certain region is driven based on driving conditions (for instance, length of voltage application) which are different from the other regions. Consequently, influence on the display caused by the temperature unevenness of the regions of the screen can be reduced, and images of favorable reproducibility can be displayed.
As a result of using the technology disclosed in Japanese Patent Application Publication No. 2007-298957, it is possible to perform the brightness correction processing in consideration of the temperature of the backlight. Specifically, as shown in FIG. 10C, the liquid crystal display apparatus may be provided with a temperature sensor for measuring the temperature of the backlight corresponding to each of blocks. Subsequently, the measured value of the brightness sensor may be corrected, for each block, according to the measured value of the temperature sensor corresponding to that block (temperature corresponding to that block). Consequently, it is possible to realize the brightness correction processing in consideration of the temperature of the backlight.
Nevertheless, as described above, the brightness correction processing (emission brightness measurement) of the respective blocks is performed in a predetermined order. Thus, with a block subject to a considerably temperature change from an ending time of the brightness correction processing to a starting time of the subsequent brightness correction processing, the brightness correction processing will be too late, and brightness unevenness (unevenness in the emission brightness of the backlight) caused by the temperature change will occur around that block. This kind of brightness unevenness will occur, for example, when the temperature changes as a result of the target brightness changing such as when the display mode of the liquid crystal display apparatus is switched.